Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/80—Mixtures of different zeolites
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
  • B01J29/068—Noble metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/08—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y
  • B01J29/10—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y containing iron group metals, noble metals or copper
  • B01J29/12—Noble metals
  • B01J29/126—Y-type faujasite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
  • B01J29/20—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type containing iron group metals, noble metals or copper
  • B01J29/22—Noble metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
  • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
  • B01J29/44—Noble metals
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
  • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
  • B01J2229/10—After treatment, characterised by the effect to be obtained
  • B01J2229/16—After treatment, characterised by the effect to be obtained to increase the Si/Al ratio; Dealumination
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/08—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y
  • B01J29/084—Y-type faujasite
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J29/00—Catalysts comprising molecular sieves
  • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
  • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
  • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the present invention relates to a catalyst for purifying the exhaust gases from diesel engines which contain one or more zeolites and at least one platinum group metal.
• the present invention relates to a method of using the catalysts as described herein for the purification of diesel engine exhaust.
• the exhaust gases from diesel engines contain carbon monoxide, unburnt hydrocarbons, nitrogen oxides and particles of soot as air pollutants.
• the unburnt hydrocarbons include paraffins, olefins, aldehydes and aromatic compounds.
• diesel exhaust gases contain a substantially higher proportion of long-chain paraffins which are difficult to oxidize.
• diesel exhaust gases are substantially colder than the exhaust gases from gasoline engines and contain oxygen at a concentration between 3 and 10 volume percent.
• the high oxygen concentration relates to the fact that diesel engines are operated with a large air/fuel ratio (kilograms of air to kilograms of fuel) of more than 18.
• Gasoline engines in contrast, operate with an air/fuel ratio of 14.6, which enables stoichiometric combustion of hydrocarbons.
• the exhaust gases from gasoline engines therefore contain virtually no oxygen.
• the exhaust gas temperature in a diesel engine When operated under part-load, the exhaust gas temperature in a diesel engine is in the range 100 to 250° C. and achieves a maximum temperature of 500 to 650° C. only when operated under full load. In contrast, the exhaust gas temperature in a gasoline engine is between 400 and 450° C. under part-load and can rise to 1000° C. under full load.
• VOC volatile organic components
• DE 39 40 758 A1 describes a catalyst for the oxidative purification of exhaust gases from diesel engines with high conversion rates for hydrocarbons and carbon monoxides at low temperatures and an inhibited oxidizing effect toward nitrogen oxides and sulphur dioxide.
• the active component in the catalyst consists of platinum, palladium, rhodium and/or iridium placed in contact with vanadium or an oxidic vanadium compound.
• the active component is deposited into finely divided aluminum oxide, titanium oxide, silicon oxide, zeolite or mixtures of these.
• the catalyst is applied in the form of a coating onto channels which allow the free passage of gases in a honeycomb shaped support made of ceramic or metal.
• the light-off temperatures T 50% of this catalyst for carbon monoxide and hydrocarbons are in the range of 210 to 275° C. (The light-off temperatures T 50% are the temperatures of the exhaust gas at which just 50% of the pollutants are converted into harmless components.) At 350° C. the catalyst exhibits good conversion rates for carbon monoxide and hydrocarbons.
• the catalyst allows nitrogen oxides to pass through virtually unchanged. Sulphur dioxide is oxidized to sulphur trioxide to only a very small extent. As a result of the dimininished oxidizing effect toward sulphur dioxide, this catalyst also leads to lower particle emissions than other oxidizing catalysts since less sulphate is available for adsorption onto the soot cores in the exhaust gases.
• EP 0 427 970 A2 describes a catalyst for reducing the amount of nitrogen oxides in an oxidizing exhaust gas with an air/fuel ratio of 22.
• the catalyst contains at least one zeolite with a molar ratio SiO 2 /Al 2 O 3 of more than 10 and pore diameters of 0.5 to 1 nm.
• Platinum groups metals are deposited on the zeolites, wherein, for each platinum group metal, a minimum ratio by weight of metal to zeolite should not be undershot if good conversion rates for nitrogen oxides are still to be obtained even after aging of the catalyst.
• DE 44 35 073 A1 describes a catalyst which contains a mixture of at least two zeolites with different pore diameters and also cerium oxide loaded with palladium.
• the mixture of zeolites is used to adsorb the differently sized hydrocarbon molecules in the exhaust gas during the cold-start phase.
• Palladium and cerium oxide are used to convert the adsorbed hydrocarbons into harmless constituents.
• An object of the present invention is to provided an improved catalyst, as compared with the prior art, for purifying the exhaust gases from diesel engines, which is capable of oxidizing in particular long-chain paraffins which are difficult to oxidize in the exhaust gas at temperatures below 200° C., and simultaneously of reducing nitrogen oxides, despite the high oxygen content of the diesel exhaust gas.
• a catalyst and method for purifying the exhaust gases from diesel engines wherein the catalyst comprises one or more zeolites and at least one platinum group metal.
• the catalyst is characterized in that it also contains one or more additional metal oxides selected from the group consisting of aluminum silicate, aluminum oxide and titanium oxide, wherein the aluminum silicate has a ratio by weight of silicon dioxide to aluminum dioxide of 0.005 to 1.
• the platinum group metal is deposited on only these additional metal oxides.
• the catalyst contains, in addition to zeolites, other metal oxides which act as a support for the platinum groups metals. It is essential for purposes of this invention that the platinum group metals are deposited only on these additional metal oxides and not on the zeolites. Deposition of the platinum group metals on the zeolites leads to less active catalysts (see comparison Example C1).
• Deposition of the platinum group metals on the additional metal oxides may be performed in a variety of ways. It is important that the method of deposition selected ensures production of the most uniformly and finely distributed deposit of platinum group metals possible on the additional metal oxides.
• One possible method of deposition is to impregnate the additional metal oxides, before mincing with the zeolites, with a solution of soluble precursors of the platinum group metals.
• Aqueous solutions are preferably used for this purpose.
• Suitable precursors of platinum group metals are any common salts and complex salts of the same. Examples of such compounds are hexachloroplatinic acid, tetrachloroplatinic acid, diammine-dinitroplatinum(II), tetraammineplatinum(II) chloride, ammonium tetrachloroplatinate(II), ammonium hexachloroplatinate(IV), platinum ethylenediamine dichloride, tetraammineplatinum(II) nitrate, tetraammineplatinum(II) hydroxide, methylethanolamine platinum(II) hydroxide, platinum nitrate, palladium chloride, palladium nitrate, diamminedinitropalladium(II), tetraammine-palladium(II) hydroxide and hexachloroiridium acid.
• the additional metal oxides are placed in contact with an aqueous solution of the platinum group metal(s), with constant stirring, so that a moist powder is produced.
• the volume of solvent is selected to correspond to about 100 to 130, preferably 110% of the water absorption capacity of the metal oxide powder being impregnated.
• the powder produced is calcined in air at 200 to 500, preferably 300° C. for 1 to 4 hours and then reduced in a hydrogen-containing stream of gas, preferably forming gas comprising 95 vol. % of nitrogen and 5 vol. % of hydrogen.
• temperatures in the range of 300 to 600° C., preferably 500° are used. Reduction is complete after about 1 to 3 hours. Investigations using an electron microscope show that the platinum group metals deposited on the specific surface area of the metal oxides are finely distributed with crystallite sizes between 10 and 50 nm.
• the additional metal oxides can be coated with a concentration of 0.01 to 5 wt. % of platinum group metal, with reference to the total weight of impregnated metal oxides.
• the additional metal oxides may be coated with vanadium at the same time as with the platinum group metals or in any sequence with these.
• further base metals such as nickel and copper may be deposited onto the additional metal oxides in order to have an effect on the catalytic activity of the platinum group metals. Soluble precursors of these metals are used for this purpose.
• the additional metal oxides act as carrier material for the catalytically active platinum group metals.
• Particularly suitable metal oxides are those which have a high specific surface area of more than 10 m 2 /g.
• active aluminum oxides These have the crystal structures of the transition series of crystallo-graphic phases of aluminum oxide which are passed through when aluminum oxide/hydroxide such as, for example, gibbsite or boehmite, are calcined at up to more than 1000° C. In detail these are chi, eta, gamma, kappa, delta and theta-aluminum oxide.
• Their specific surface areas may be several hundred square meters per gram.
• These materials may be doped with, for example, rare earth oxides, in order to stabilize their specific surface areas.
• Titanium oxides produced in a wet-chemical process largely possess the crystal structure of anatase and have specific surface areas of usually more than 50 m 2 /g. Titanium oxides produced by flame hydrolysis have a mixed structure of about 70% anatase and 30% rutile. The specific surface area of these so-called pyrogenic titanium oxides is about 50 m 2 /g.
• aluminum silicate is preferably used as support material for the platinum group metals.
• the material is a special aluminum silicate which has a ratio by weight of silicon dioxide to aluminum oxide of 0.005 to 1 and a very homogeneous distribution of aluminum oxide and silicon dioxide.
• the crystal structure of this aluminum silicate in contrast to the zeolite, is boehmitic and becomes amorphous with increasing amounts of silicon dioxide.
• the specific surface area of this aluminum silicate depending on the concentration of silicon dioxide, is 200 to 500 m 2 /g and exhibits exceptional surface area stability under the operating conditions obtained during purification of diesel exhaust gases. Table 1 shows these properties.
• a specific concentration of metal crystallites is obtained per square meter of specific surface area of aluminum silicate for a given loading of the aluminum silicate (for example, 1.5 wt. % of Pt with reference to the total weight of aluminum silicate and platinum).
• the crystallite concentration can be increased for the same loading by decreasing the specific surface area of the aluminum silicate.
• Aluminum silicates of a given composition but with different specific surface areas can thus be prepared by calcination.
• materials with a specific surface area greater than 100 m 2 /g are preferably used.
• the platinum concentration in mg of Pt per square meter of specific surface are (in the freshly prepared state) is given in the last column of Table 1, calculated for the case of loading the aluminum silicate with 1 wt. % of platinum. It can be seen that, for a given composition of aluminum silicate (e.g., 95 Al 2 O 3 /5 SiO 2 ) and a given platinum loading (e.g., 1 wt. %), the platinum concentration on the specific surface area, and thus the crystallite concentration, can be affected by varying the specific surface area.
• These aluminum silicates may optionally contain homogeneously incorporated elements which form oxides stable at high temperatures. Suitable elements are, for example, the rare earths such as lanthanum and cerium as well as zirconium and the alkaline earth metals, which are incorporated in the form of appropriate precursors. Concentrations of up to 10 wt. %, calculated as the oxide of these elements are preferred. High concentrations of alkali metals such as, for example, sodium have proven to be unsuitable. Particularly suitable aluminum silicates have a concentration of sodium, calculated as the oxide, of preferably less than 75 ppm.
• a particularly suitable aluminum silicate is described in DE 38 39 580 C1.
• the aluminum silicate is obtained by mixing an aluminum compound with a silicic acid compound in aqueous medium, drying and optionally calcining the product.
• the aluminum compound used is a C 2 -C 20 -aluminum alcoholate which is hydrolyzed with water purified by passage through an ion exchanger.
• 0.1 to 5.0 wt. % of orthosilicic acid, purified by passage through an ion exchanger are added to the hydrolysis water.
• 0.1 to 5.0 wt. % of orthosilicic acid, purified by passage through an ion exchanger are added to the alumina/water mixture obtained by neutral hydrolysis.
• This particularly preferred aluminum silicate may contain lanthanum oxide or also other rare earth oxides.
• the zeolites used in the catalyst according to the invention must have a modulus greater than 10 in order to be sufficiently stable toward the acid components in the exhaust gas and to the maximum exhaust gas temperature.
• Suitable zeolites are, for example, ZSM5, mordenite and dealuminized Y-zeolite (DAY). They may be used in the Na + or H + form.
• Zeolites can be described by the general formula:
• x is the so-called modulus of the zeolite and which is the molar ratio of silicon dioxide to aluminum oxide. Taking into account the molar weights, zeolites therefore have a ratio by weight of silicon dioxide to aluminum oxide of more than 1.18. Zeolites with a modulus of greater than 10, i.e., with a ratio by weight of silicon dioxide to aluminum oxide of greater than 5.9 are preferably used for the catalyst according to the invention. A ratio of this size ensures adequate stability of the characteristic crystal structure of the zeolites at the temperatures in diesel exhaust gases and at the concentrations of acid pollutants contained in them.
• a zeolite mixture of at least two zeolites is used, one having a modulus of less than 50 and the other a modulus of more than 200. It has been shown that the broadest possible spectrum of modules for the zeolites used has an advantageous effect on the conversion rates of the pollutants.
• a dealuminizing treatment it is possible to prepare zeolites of one structural type with a broad spectrum of modules.
• the modulus of a ZSM5 zeolite with a stoichiometric composition, for example has a value of 5.
• the modulus values can be adjusted to more than 1000. Similar behavior is shown by Y-zeolites and mordenite. Table 2 lists the properties of some zeolites which are suitable for the catalyst according to the invention.
• a mixture of the 5 zeolites cited in Table 2 is preferably used in the catalyst according to the invention.
• the ratio by weight of the zeolites with respect to each other can be varied over wide limits. However, a mixture with equal parts by weight of all the zeolites is mainly used.
• a platinum activated aluminum silicate is combined with a zeolite mixture of a dealuminized Y-zeolite and a Na-ZSM5 zeolite whose moduli are greater than 120.
• a particularly low light-off temperature for the conversion of carbon monoxide is obtained if an aluminum silicate with a specific surface area between 100 and 200 m 2 /g and with a platinum loading between 0.05 and 0.2 mg Pt/m 2 is used.
• Particularly suitable for this purpose is an aluminum silicate with a SiO 2 content of about 5 wt.
• the low light-off temperature under part-load is in the range 100 to 150° C. In this temperature range, a small reduction in the light-ff temperature represents a clear improvement in pollutant conversion.
• the zeolite mixture is mixed with the catalytically activated additional metal oxides.
• ratios by weight of metal oxides to zeolite mixture of 10:1 to 1:3, preferably 6:1 to 2:1, are used.
• the zeolite mixture in the catalyst has the main task of storing the hydrocarbons in the exhaust gas at low exhaust gas temperatures ( ⁇ 150-200° C.) in order to release them again under operating conditions for the diesel engine with higher exhaust gas temperatures.
• the desorbed hydrocarbons are partially oxidized by the catalytically activated additional metal oxides to give carbon monoxide and water.
• the non-oxidized fraction of the hydrocarbons acts, in addition to carbon monoxide, as a reducing agent for the catalytic reduction of nitrogen oxides contained in the exhaust gas.
• the resulting catalyst mixture can be processed by adding appropriate auxiliary agents such as inorganic binders (e.g., silica sol), pore producers, plasticizers and moistening agents in a known way to give molded items such as tablets and extrudates.
• auxiliary agents such as inorganic binders (e.g., silica sol), pore producers, plasticizers and moistening agents in a known way to give molded items such as tablets and extrudates.
• the catalyst is applied in the form of a coating to the internal walls of the flow channels in the honeycomb carriers.
• honeycomb carrier volume For exhaust gas purification of diesel engines, amounts of coating of 50 to 400 g/l of honeycomb carrier volume are required.
• the composition of the catalyst should be adjusted so that the catalytically active components on the additional metal oxides are present at a concentration of 0.01 to 5 g/l of honeycomb carrier volume.
• the coating procedures required are known to a person skilled in the art.
• the catalyst mixture of activated metal oxides and zeolite mixture are processed to give nan aqueous coating dispersion.
• Silica sol for example, may be added to this dispersion as a binder.
• the viscosity of the dispersion may be adjusted by suitable additives so that it is possible to apply the required amount of coating to the walls of the flow channels in a single working process. If this is not possible, the coating procedure may be repeated several times, wherein each freshly applied coating is fixed by an intermediate drying process.
• the final coating is then dried at elevated temperature and calcined in air for a period of 1 to 4 hours at temperatures between 300 and 600° C.
• the coating honeycomb carrier was then impregnated with an aqueous solution of tetra-ammine-platinum(II) hydroxide dried at 150° C. in air and calcined at 250° C.
• the final catalyst contained 120 g of oxide and 1.77 g of platinum per liter of honeycomb carrier volume.
• the open-celled honeycomb carrier consisted of cordierite with a diameter of 2.5 cm, a length of 7.6 cm and 62 cells or flow channels per cm 2 , the flow channels having a wall thickness of 0.2 mm.
• a comparison catalyst was prepared as follows, in accordance with DE 39 40 758 A1, Example 18.
• An aqueous coating dispersion with a solids content of 40% was made up.
• the dispersion contained, with reference to dry substance, 60 wt. % of ⁇ -aluminum oxide (180 m 2 /g specific surface area) and 40 wt. % of titanium dioxide (50 m 2 /g specific surface area).
• a honeycomb carrier was coated with the metal oxides by immersion in the coating dispersion and afterwards dried at 120° C. in the air. After calcining for 2 hours at 400° C., the coated honeycomb carrier was impregnated with an aqueous solution of tetraamineplatinum(II) hydroxide dried at 150° C.
• the catalyst precursor obtained in this way was reduced for a period of 2 hours at 500° C. in a stream of forming gas (95% N 2 , 5% H 2 ) .
• the final catalyst contained, per liter of honeycomb carrier volume, 64 g of titanium dioxide, 96 g of aluminum oxide, 5 g of vanadium oxide and 1.77 g of platinum.
• a comparison catalyst was prepared as follows, in accordance with DE 39 40 758 A1.
• An aqueous coating dispersion with a solids content of 40% was made up.
• the dispersion contained, with reference to dry substance, 95 wt. % of ⁇ -aluminum oxide (180 m 2 /g specific surface area) and 5 wt. % of silicon dioxide (100 m 2 /g specific surface area).
• a honeycomb carrier was coated with the metal oxides by immersion in the coating dispersion and afterwards dried at 120° C. in air. After calcining for 2 hours at 400° C., the coated honeycomb carrier was impregnated with an aqueous solution of hexachloroplatinic acid, dried at 150° C.
• the catalyst precursor obtained in this way was reduced for 2 hours at 500° C. in a stream of forming gas (98% N 2 , 5% H 2 ).
• the final catalyst contained, per liter of honeycomb carrier, 200 g of oxide and 1.77 g of platinum.
• a comparison catalyst was prepared as follows, in accordance with DE 44 35 073 A1, Example 13. First, cerium dioxide with a specific surface area of 105 m 2 /g was impregnated with palladium. For this, the cerium dioxide was placed in contact with an aqueous solution of tetraammine-platinum(II) nitrate, with constant stirring, so that a moist powder was produced. After drying for two hours at 120° C. in air, the powder produced was calcined for 2 h at 300° C. in air. The Pd-cerium oxide powder contained, with reference to the total weight, 1.47 wt. % of palladium.
• An aluminum silicate with 5 wt. % of silicon dioxide (spec. surface area 286 m 2 /g; see Table 1) was activated with platinum for the catalyst according to the invention.
• the aluminum silicate was placed in contact with an aqueous solution of tetraammineplatinum(II) hydroxide, with constant stirring, so that a moist powder was produced.
• the powder produced was calcined at 2 h at 300° C. in air.
• Reduction in a stream of forming gas (95 vol. % N 2 and 5 vol. % H 2 ) was performed at 500° C. for a period of 2 h.
• the Pt-aluminum silicate powder contained, with reference to the total weight, 1.47 wt. % of platinum.
• This honeycomb carrier was coated with an amount of 180 g of oxides per liter of honeycomb carrier volume, by immersion in the coating dispersion. The coating was dried for 2 hours at 120° C. in air and then calcined for 2 h at 500° C. The final catalyst contained, per liter of catalyst volume, 1.77 g of platinum.
• a further catalyst in accordance with Example 1 was made up. Instead of the zeolite mixture, only Na-ZSM5 (x>1000) in amount of 33 wt. %, with reference to the total weight of catalyst mixture, was used.
• the aluminum silicate was coated with 2.94 wt. % of platinum.
• the precise composition of the catalyst can be obtained from Table 4.
• Example 7 Another catalyst analogous to Example 7 was made up, but with a ratio by weight of Pt-aluminum silicate to zeolite mixture of 5:1.
• a catalyst according to Example 13 with 0.18 g of Pt per liter of honeycomb carrier was also coated, along 30% of its length, with the coating dispersion for the catalyst in Example 9.
• the additional coating was applied at a concentration of 39 g/l of honeycomb carrier volume.
• the final catalyst contained 209 g of oxides per liter of honeycomb carrier and had a concentration of 0.72 g Pt/l.
• Example 15 The additional coating on the catalyst in Example 15 was applied each time to 15% of the length of the honeycomb carrier starting from a front face of the honeycomb carrier.
• a catalyst was made up according to Example 10 with 1.41 g Pt/l of honeycomb carrier, but using only 60 g/dm 3 of aluminum silicate.
• a catalyst with 140 g/l Pt-aluminum silicate and 100 g/l of zeolite mixture was made up.
• the platinum content of the Pt-aluminum silicate was 1.0 wt. %.
• the final catalyst contained 1.41 g Pt/l.
• a catalyst was prepared according to Example 10. An aqueous solution of hexachloroplatinic acid was used to activate the aluminum silicate.
• a catalyst was prepared according to Example 10. An aqueous solution of platinum (II) nitrate was used to activate the aluminum silicate.
• a catalyst was prepared according to Example 9. Palladium, incorporated using an aqueous solution of palladium(II) nitrate, was used to activate the aluminum silicate.
• a catalyst was prepared according to Example 1. A mixture of platinum and rhodium in the ratio of 5:1 was used to activate the aluminum silicate. Hexachloroplatinic acid was used as a precursor for platinum and rhodium(III) chloride was used as a precursor for rhodium.
• a catalyst according to Example 1 was prepared. A mixture of platinum, palladium and rhodium in the ratio of 10:1:3 was used to activate the aluminum silicate. Tetraamineplatinum(II) hydroxide was used as a precursor for platinum, palladium(II) nitrate as a precursor for palladium and rhodium(II) nitrate as a precursor for rhodium.
• a catalyst according to Example 10 was prepared.
• An aqueous solution of methylethanoloamine-platinum(II) hydroxide was used to activate the aluminum silicate.
• a catalyst according to Example 1 was prepared. Differently from Example 1, the aluminum silicate activated with platinum was not reduced in a stream of forming gas, but was only calcined in air for 2 hours at 600° C.
• a catalyst according to Example 1 was prepared, but the Pt-aluminum silicate was not dried and calcined or reduced after impregnation, but was mixed immediately with zeolite mixture and processed to form a coating dispersion.
• the aluminum silicate was dispersed in an aqueous solution of platinum (II) nitrate. Then the pH of the dispersion was increased to 9 by adding an aqueous, concentrated ammonia solution. Then the zeolite mixture was stirred into the dispersion. The final dispersion had a solids content of 40 wt. %.
• a catalyst according to Example 28 was prepared. Instead of platinum(II) nitrate, an aqueous solution of tetraammineplatinum (II) nitrate was used. Adjustment of the pH to 2 was achieved by adding a saturated aliphatic monocarboxylic acid.
• a catalyst according to Example 17 was prepared. Instead of the ceramic honeycomb carrier of cordierite, a likewise open-celled, honeycomb-shaped, metal carrier with a diameter of 2.5 cm, a length of 7.5 cm and 62 cells or flow channels per cm 2 , the flow channels having a wall thickness of 0.4 mm, was used.
• a catalyst according to Example 9 was prepared. Instead of the aluminum silicate, a ⁇ -aluminum oxide with a specific surface area of 188 m 2 /g was used.
• a catalyst according to Example 9 was prepared. Instead of the aluminum silicate, titanium oxide with a specific surface area of 95 m 2 /g was used.
• a catalyst according to Example 1 was made up, but with the following modifications.
• An aluminum silicate with a specific surface area reduced to 153 m 2 /g by calcination was used (see Table 1).
• This material was impregnated with methylethanolamine platinum(II) hydroxide in the same way as in Example 26.
• the zeolite mixture selected was a mixture of DAY and Na-ZSM5.
• the ratio by weight of aluminum silicate to zeolites was adjusted to 6:1.
• the amount of coating per liter of honeycomb carrier volume was 140 g.
• the catalyst was finally reduced for 2 hours in a stream of forming gas at 500°0 C.
• the final catalyst contained 1.36 g of platinum per liter of catalyst volume.
• a catalyst according to Example 33 was prepared.
• An aqueous solution of tetraammineplatinum(II) nitrate was used to activate the aluminum silicate.
• a catalyst according to Example 34 was prepared.
• An aluminum silicate with 5 wt. % of silicon dioxide and a specific surface area of 212 m 2 /g (see Table 1) was used as support oxide.
• a catalyst according to Example 34 was prepared.
• An aluminum silicate with 5 wt. % of silicon dioxide and a specific surface area of 320 m 2 /g (see Table 1) was used as support oxide.
• a catalyst according to Example 36 was prepared.
• An aluminum silicate with 10 wt. % of silicon dioxide and a specific surface area of 163 m 2 /g (see Table 1) was used as support oxide.
• the catalytic activity of the exhaust gas purification catalysts in the preceding examples was measured in a synthesis gas unit. Using this unit, it is possible to simulate all the gaseous exhaust gas components present in the actual exhaust gas from a diesel of a gasoline engine.
• the test conditions selected and the model gas composition are given in Table 5. Normal- hexadence, trivial name cetane, which is known as a reference substance for determining the ignition performance of diesel fuels, was used as the hydrocarbon component. Considerable amounts of this long-chain, aliphatic compound are also found in actual diesel exhaust gas.
• the exhaust gas was heated at a rate of 15° C./min.
• the conversion of nitrogen oxides was determined at an exhaust gas temperature of 200° C.
• German priority application 196 14 540.6 is relied on and incorporated herein by reference.

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